Intermittent hypoxia (IH) is a frequent condition in clinical medicine (e.g., sleep apnea, SIDS), which bears substantial morbidity and mortality. Furthermore, organismal adaptations to IH suggest the formation of specific forms of neuronal plasticity. While substantial study of the effects of IH has been performed in the mature mammal, little if any work has been done during the early phases of post-natal development, a unique period of neuronal vulnerability and adaptation. Therefore, we hypothesized that post-natal intermittent hypoxia, such as occurs in sleep apnea, may impose long-term modifications in respiratory control, thereby leading to a form of metaplasticity of respiratory patterning. The latter modification of the respiratory network induced by early post-natal IH could impose either a functionally favorable or a maladaptive alteration of the respiratory response system. To examine this issue, we will: (i) characterize the effects of post-natal IH on normoxic ventilation and on hypoxic and hypercapnic ventilatory responses in freely behaving rats.; (ii) assess the effects of IH on phrenic motor nerve long-term facilitation (LTF).; (iii) determine the potential role of signaling pathways, particularly protein kinase C (PKC), in the long-term modification of ventilation imposed by IH through development. This work will therefore contribute to the understanding of potential mechanisms mediating not only early adaptations to IH but also provide insights to long-lasting changes in ventilation that may develop when a conditioning stimulus is applied during critical phase of maturation. [unreadable] [unreadable]